This invention relates to air purged shaft seal assemblies for use, for example with mixers and especially mixers which are used to mix abrasive products such as sugar or concrete mixes.
It is known to use packing glands or lip seals with or without air purging in shaft seal assemblies, but known shaft seal assemblies of the kind have not proved to be particularly successful in practice because frequent servicing thereof by replacement of warn packing glands or lip seals is required.
It is therefore an object of the invention to provide an air purged shaft seal assembly with improved life before servicing becomes necessary.
According to the invention, an air purged shaft seal assembly has a seal housing fixedly securable to a stationary support having a circular aperture through which a shaft can pass. The seal housing has an internal annular surface defining the circular aperture, the internal annular surface having a first annular portion for engaging an outer surface of an annular sealing member and a second annular portion shaped to partially form an air receiving chamber, the seal housing having a passage for supplying air under pressure from an external source thereof to an air receiving chamber.
A sleeve is mountable on the shaft for sliding movement therealong, the sleeve having an external peripheral surface with a first peripheral portion co-operable with the first annular portion of the internal annular surface of the seal housing to receive the annular sealing member therebetween and a second peripheral portion co-operable with the second annular portion of the internal annular surface of the seal housing to form the air receiving chamber. A shaft collar surrounds and is fixedly securable to the shaft and means are provided to cause the sleeve to rotate with the shaft and the shaft collar.
The shaft collar carries sleeve adjustment means to enable the sleeve to be moved longitudinally on the shaft to adjust the distance between a portion of the seal housing and a portion of the sleeve adjacent the air receiving chamber to provide an adjustable annular gap therebetween to enable air under pressure to escape from the air receiving chamber and prevent foreign material from passing into the air receiving chamber between said portions of the seal housing and the sleeve adjacent thereto.